1. Related Applications
This invention is related to Non-Provisional application Ser. No. 11/286,792, now U.S. Pat. No. 7,343,265, by Andarawis, et al., titled “System to Monitor the Health of a Structure, Sensor Nodes, Program Product, and Related Methods,” filed on Nov. 23, 2005, and Non-Provisional application Ser. No. 11/287,009., now U.S. Pat. No. 7,276,703 by Berkcan, et al., titled “System to Monitor the Health of a Structure, Sensor Nodes, Program Product, and Related Methods,” filed on Nov. 23, 2005, all incorporated by reference herein in their entirety.
2. Field of the Invention
The present invention relates generally to multi-node sensor systems. More specifically, the present invention relates to a system, sensor nodes, program product, and related methods to monitor the health of structural components and to reduce an amount of data required to be communicated.
3. Description of the Related Art
Various types of platforms such as, for example, aircraft structural components, aircraft skins, or other related components when in operation are subjected to various environmental conditions such as stress and strain, exposure to temperature extremes, and/or significant vibration energy. Due to the various environmental conditions such components can suffer material degradation over time.
Structural health monitoring helps promote realization of the full potential of such components. Remotely positioned sensors have been installed adjacent to such structures/components to monitor various parameters such as, for example, strain levels, stress, temperature, pressure, or vibration level to help manage physical inspection schedules, maintenance schedules, to help predict material failure, and generally monitor the “health” of such components. Such sensors have been provided a dedicated power supply such as power obtained through conductors, e.g., wires, connected to the aircraft electrical system or through chemical batteries. Such wiring can, in some instances, undesirably result in increased weight and complexity of the component being monitored and/or or the associated structure or component and are subject to damage or breakage requiring extensive repair costs and down time. Depending upon available space, batteries can be inappropriate due to their size. Batteries, which can also have a limited service life and, therefore, which typically require periodic inspection and/or replacement, are often positioned in locations difficult to reach, and often require costly disassembly and reassembly of the sensor or component to perform service on the battery. Further, batteries may not be suitable due to environmental constraints, i.e., temperature changes often affect battery performance.
Some more recent monitoring systems include fiber-optic sensors connected to a network of fiber-optic conductors to form an interrogation system. Such fiber-optic conductors, as with electrical conductors, can significantly raise the complexity of the component and/or deployment of the sensor system. Other monitoring systems include self-powered sensors attached to or embedded within the components to be monitored that can reduce dependence on batteries or any other external power source. Such sensors can be relatively small in size and can utilize, as a power source, energy obtained or otherwise transmitted through the component or structure being monitored.
Such devices can include those known as micro-electro-mechanical systems (MEMS). This type of sensor can typically consume very low amounts of power in the microwatt range. Other such devices can also include those known as piezoelectric devices. Some related piezoelectric devices can be in the form of actuators which can apply a force on the skin structure to dampen detected vibrations. Still other monitoring systems can include both active and passive wireless sensors attached to or embedded within the component or structure. The active wireless sensors can actively or passively collect and actively provide a continuous or intermittent stream of sampled raw data indicating parameters of the component or structure being monitored. The sensor data is typically collected by a central collector or by a series of intermediate collectors which provide such data to a central collector. The passive wireless sensors can also collect data with respect to parameters of the component or structure being monitored. The passive sensors, however, receive energy from, for example, a mobile vehicle or handheld base device or reader positioned adjacent each wireless sensor to provide power to extract the sensor data. The reader can transmit a signal to each wireless sensor to power the sensor and to transmit a request for data. In response to the signal from the reader, the wireless sensor can vary impedance of a wireless antenna, which the reader detects and uses to receive raw sensor data.
Such wireless devices attached to or embedded within the component or structure being monitored can have limitations on available power and communication bandwidth for reporting sensed data. Communicating raw sensor data places a significant burden on the communication system to accommodate the data transfer. Low sampling rate is typically employed to alleviate the data communication issues.
In view of the foregoing, it would be desirable to provide a sensor system that provides data reduction and/or compression schemes to reduce the amount of data that needs to be communicated and/or stored and to reduce power requirements in performing such communication and/or data storage. Further, it would be desirable to provide simple data reduction methods to reduce processing requirements in order to simplify the design of such sensors and to reduce such power requirements thereof.